1. Field of the Invention
The present invention relates to an image forming apparatus and a foreign matter removing method.
2. Description of Related Art
In conventional image forming apparatuses, foreign matter such as toner that is attached on the surface of an image carrier such as an intermediate transfer belt or a photoreceptor drum is scraped and removed after image transfer by means of a blade (abutting member) of a cleaning device that abuts the image carrier.
However, when a large number of sheets of recording media is processed for example, the toner that has been accumulated at the abutment part between the blade and the image carrier may sometimes leak to the back face of the blade at the downstream side in the rotational direction of the image carrier, and the leaked toner may be gradually accumulated onto the back face of the blade. Then, when the toner on the back face of the blade transfers back to the image carrier, it causes an image defect.
To avoid this, it is possible to attach the toner and the like accumulated on the blade onto the surface of the image carrier by separating the developer from the image carrier and forming a potential pattern on the surface of the image carrier in which a first potential and a second potential lower than the first potential are alternately distributed in the rotational direction of the image carrier, and to collect them by means of a collector (e.g. the developer). The occurrence of image defect can thus be prevented (see JP 2007-094283A).
However, in typical image forming apparatuses that do not have a structure to separate a developer from an image carrier, the developing bias (potential between the image carrier and the developer) cannot be controlled to follow the potential pattern when the potential pattern of the alternating first and second potentials has a short cycle. Accordingly, it is required to employ a technique that is applicable in the condition that the developing bias is fixed at a certain level.
However, a problem with fixing the developing bias at a certain level is the increased fog margin (difference between the first potential of the image carrier and the potential of the developing bias). For example, when the fog margin is increased to “−150 V or more”, a phenomenon of a carrier adhering to the image carrier, also known as beads carry over, occurs, which results in internal contamination of the image forming apparatus, damage of the image carrier and the like.
In contrast, when the fog margin (difference between the first potential of the image carrier and the potential of the developing bias) is maintained at a low level, for example in the range of approximately “−100 V to −150V”, it is possible to prevent the occurrence of beads carry over. However, the potential difference between the second potential of the image carrier and the developing bias is increased compared to the former case. Since toner is transferred to the image carrier according to the significance of the potential difference, a problem with this case is an increased amount of toner consumed. Furthermore, another problem is that a large amount of toner transferred to the image carrier causes imperfect cleaning.
It is an object of the present invention to provide an image forming apparatus and a foreign matter removing method that can remove foreign matter such as toner attached to a blade without causing beads carry over or increasing the toner consumption.